PROBLEM I. How Simple Animals mni Flams Reproduce 419 



entrance of dust and bacteria. How can you be sure that the broth in the 

 tubes is sterile? Allow several of the tubes to stand open exposed to the air 

 of the classroom after the broth has cooled to 80° F or below. If possible 

 keep all tubes at a temperature of 80° F. Examine after 72 hours. What do 

 you notice? 



2. How do paramecia reproduce? Examine a rich culture under low- 

 power. Look for dividing forms. What shape are they? Draw a few im- 

 portant stages in their reproduction. Now examine a prepared slide of 

 division in Paramecium. Use the high power. What must you now add to 

 your drawings to complete them? What is this type of reproduction 

 called? Do all the cells divide lengthwise, crosswdse, or some lengthwise 

 and some crosswise? 



3. How does the yeast plant reproduce? Stir a small amount of yeast 

 into a flask of dilute sugar water. Allow it to stand for a day at room tem- 

 perature. Mix a bit of yeast cake in half a tumbler of plain water and ex- 

 amine a drop under high power. (You may need assistance in finding the 

 cells.) Draw^ one or two yeast cells much enlarged. Now examine a drop 

 of the mixture of sugar water and yeast under the high powder. Compare 

 with the yeast plants studied first. Why would you expect this yeast to 

 be reproducing? How does it reproduce? You will not see a nucleus in 

 these cells with an ordinary school microscope. Label "mother" and 

 "daughter" cells in your diagram. 



4. How does bread mold reproduce? Place a slice of bread on moist 

 blotting paper in a dish and sprinkle some dust on it. Cover and put it 

 away in a dark warm place. Examine it morning and evening for several 

 days. When threads begin to appear, observe them closely with a magnify- 

 ing glass and take notes. What color are the threads or hyphae? What do 

 you see on the ends of some of the hyphae? How do these ends change 

 after some days? These structures contain tiny spores that may grow into 

 new hyphae. What makes the bread mold look black? How does the 

 bread mold get the food used in this growth? 



5. Mold reproduction studied with a microscope. Examine a bit of the 

 mold mounted in a drop of water under the low power of the microscope. 

 Can you find structures which seem to hold the mold to the bread and 

 absorb food? Examine spore cases. Do you see anything that suggests how 

 the spores escape? Draw what you see. How is this type of reproduction 

 like and how is it unlike that of an ameba? What is it called? 



6. How does Spirogyra reproduce? If no living material showing con- 

 jugation is available, use prepared slides. Find two filaments which are 

 lying side by side. Look for cells in which a bridge is beginning to form. 

 Find a completed bridge. Do you see any cell bodies crossing from one 

 strand to the other? What can you call these? How do they get across? 

 The other cells are the passive gametes. Have any of the gametes gone 

 completely across? How do you know? Find a cell that has been formed 

 by the fusion of two gametes. Can you see the fused nucleus? Explain. 



